I&#39;ve pushed the fix.  Here&#39;s the patch, if you are curious.<br><br>--- a/Rendering/vtkImageStack.cxx<br>+++ b/Rendering/vtkImageStack.cxx<br>@@ -332,8 +332,8 @@ int vtkImageStack::RenderTranslucentPolygonalGeometry(vtkViewport* viewport)<br>

     {<br>     // no multi-pass if only one image<br>     this-&gt;Images-&gt;InitTraversal(pit);<br>-    image-&gt;SetAllocatedRenderTime(renderTime, viewport);<br>     image = this-&gt;Images-&gt;GetNextImage(pit);<br>
+    image-&gt;SetAllocatedRenderTime(renderTime, viewport);<br>
     return image-&gt;RenderTranslucentPolygonalGeometry(viewport);<br>     }<br> <br>@@ -377,8 +377,8 @@ int vtkImageStack::RenderOverlay(vtkViewport* viewport)<br>     {<br>     // no multi-pass if only one image<br>     this-&gt;Images-&gt;InitTraversal(pit);<br>

-    image-&gt;SetAllocatedRenderTime(renderTime, viewport);<br>     image = this-&gt;Images-&gt;GetNextImage(pit);<br>+    image-&gt;SetAllocatedRenderTime(renderTime, viewport);<br>     return image-&gt;RenderOverlay(viewport);<br>

     }<br>